Receiver

ABSTRACT

The receiver comprises a tuner that converts the FM radio broadcast signal into an intermediate frequency signal that is the same as a sound intermediate frequency subcarrier signal when receiving the television broadcast signal and outputs it when receiving the FM radio broadcast signal, a SAW filter passes only an intermediate frequency band out of the output of the tuner, a video detector detects a video signal containing a sound subcarrier signal when receiving the television broadcast signal and detects a sound subcarrier signal when receiving the FM radio broadcast signal, a VIFAGC circuit makes the amplitude of a video signal output at a constant value, and an AGC circuit makes the amplitude of a sound subcarrier signal outputted from a band pass filter at a constant value.

FIELD OF THE INVENTION

[0001] The present invention in general relates to a receiver by which atelevision broadcast signal and an FM radio broadcast signal can beselectively received and can be demodulated and outputted. Moreparticularly, this invention relates to a receiver which is lightweightand small in size.

BACKGROUND OF THE INVENTION

[0002] Recently, accompanied with the prevalence of a portable colortelevisions, for example liquid crystal televisions, a televisionreceiver by which receiving a general FM broadcast is possible hasappeared. This television receiver can receive sound signals of FM radiobroadcast signals by employing a high frequency circuit, such as atuner, and a sound signal demodulation circuit for a televisionbroadcast signal. When a sound signal of an FM radio broadcast signal isdemodulated, the demodulation is performed without employing a videointermediate carrier signal of a television broadcast signal.

[0003]FIG. 6 is a block diagram showing the structure of a conventionaltelevision receiver which can also receive FM radio broadcast signal.First, the occasion on which a television broadcast signal is receivedis explained. A tuner 112 is used for tuning to a television broadcastsignal received via an antenna 111. The tuner 112 down converts thereceived signal into an intermediate frequency, and outputs thisintermediate frequency band signal to SAW filters 113, 121. The SAWfilter 113 passes the intermediate frequency band having a videointermediate carrier frequency of and outputs it to a VIF amplifier 114.The VIF amplifier 114 amplifies the intermediate frequency band signaland outputs it to a video detector 116 and also to a switch 120.

[0004] The switch 120 is connected to a terminal to which the output ofthe VIF amplifier 114 is supplied when receiving the televisionbroadcast signal, and the intermediate frequency band signal isoutputted to an APC (automatic phase control circuit) 118 via the switch120. The APC 118 detects the phase difference between the videointermediate carrier frequency of in the intermediate frequency bandsignals and a signal that a voltage control oscillation circuit (VCO)117 outputs and outputs it to the VCO 117. The VCO 117 outputs thesignal of the video intermediate carrier frequency of which is phaselocked to the video intermediate carrier frequency of to the videodetector 116 based on the phase difference. The video detector 116detects a video signal based on the signal of the video intermediatecarrier frequency of that the VCO 117 outputs and outputs it to aterminal 119. The detection output of the video detector 116 isoutputted to a VIFAGC circuit 115, and the VIFAGC circuit 115 performsgain control so as to stabilize the amplitude of the detection output ofthe video detector 116 with respect to the VIF amplifier 114.

[0005] On the other hand, the SAW filter 121 passes an intermediatefrequency (of-fs), and a QIF amplifier 122 amplifies this intermediatefrequency based on the gain control by a QIFAGC circuit 123 and outputsit to an intermediate frequency detection circuit (QIFDET) 124. Theintermediate frequency detection circuit 124 mixes the inputtedintermediate frequency (of-fs) with video intermediate carrier frequencyof outputted from the VCO 117 and outputs a sound subcarrier frequencyfs. Then, the sound subcarrier frequency fs is extracted via a band passfilter 131 and is amplified by an SIF amplifier 132, and a sound signaldetected and outputted by an FM detector 133 is outputted from aterminal 134.

[0006] When receiving the FM radio broadcast signal, the tuner 112 downconverts the signal into an intermediate frequency that is the same asthe intermediate frequency (of-fs) and outputs it to the SAW filter 121.After that, the FM sound intermediate frequency fs is detected by theintermediate frequency detection circuit 124 similarly to the soundsubcarrier frequency fs, and lastly, a sound signal is outputted fromthe terminal 134. In this case, since the VCO does not output the videointermediate carrier frequency of, the switch 120 is connected to theinput side of the oscillation frequency of corresponding to the videointermediate carrier frequency of, and the oscillation frequency of isoutputted to the APC 118. With this, the VCO 117 outputs a phase lockedoscillation frequency of to the intermediate frequency detection circuit124 and detects and outputs the FM sound intermediate frequency fs.

[0007] In the conventional receiver, a video signal related intermediatefrequency processing circuit of a television broadcast signal and asound signal related intermediate frequency processing circuit of asound signal of a television broadcast signal and a sound signal of anFM radio broadcast signal are independently provided. Accordingly,demodulation characteristic of a sound signal of an FM radio broadcastsignal can be set optimally.

[0008] However, since the video signal related intermediate frequencyprocessing circuit and the sound signal related intermediate frequencyprocessing circuit are independently provided, many parts and circuitblocks have to be provided, and thus there is a problem that the costincreases and also it is impossible to obtain a lightweight and smallsize receiver.

SUMMARY OF THE INVENTION

[0009] It is an object of the present invention to obtain a receiver bywhich an FM radio broadcast signal can be received in addition to thereception of a television broadcast receiving signal and which islightweight and small in size.

[0010] In the receiver according to one aspect of this invention, whenreceiving the television broadcast signal, a first switch selects avideo intermediate carrier signal output by an intermediate frequencyamplifier and a second switch is switched towards and connected to afirst automatic gain controller. A tuner converts the televisionbroadcast signal into an intermediate frequency, and a band limit filterpasses this intermediate frequency so that the intermediate frequency isamplified by the intermediate frequency amplifier. On this occasion, theintermediate frequency amplifier is gain controlled so that theamplitude of the video signal that the video detector outputs is madeconstant by the first automatic gain controller. When receiving the FMradio broadcast, the first switch is switched towards a self-runningoscillation signal, and the second switch is switched towards andconnected to a second automatic gain controller. The tuner converts theFM radio broadcast signal into an intermediate frequency that is thesame as the sound intermediate frequency subcarrier signal whenreceiving the television broadcast signal and outputs it when receivingthe FM radio broadcast signal. The band limit filter passes thisintermediate frequency, and the intermediate frequency is amplified bythe intermediate frequency amplifier. On this occasion, the intermediatefrequency amplifier is gain controlled so that the amplitude of thesound subcarrier signal that the sound band limit filter outputs is madeconstant by the second automatic gain controller. With this, the bandlimit filter of the exclusive use of sound, the intermediate frequencyamplification circuit of the exclusive use of sound, and theintermediate frequency detection circuit of the exclusive use of soundbecome unnecessary, and a sound signal having a high quality can bedemodulated and outputted even when receiving the FM radio broadcastsignal.

[0011] In the receiver according to another aspect of this invention,when receiving the television broadcast signal, a first switch selects avideo intermediate carrier signal output by an intermediate frequencyamplifier, and a second switch is switched towards and connected to afirst automatic gain controller. A tuner converts the televisionbroadcast signal into an intermediate frequency, and a band limit filterpasses this intermediate frequency so that the intermediate frequency isamplified by the intermediate frequency amplifier. On this occasion, theintermediate frequency amplifier is gain controlled so that theamplitude of the video signal that the video detector outputs is madeconstant by the first automatic gain controller. After that, the videodetector outputs the video signal containing the sound subcarrier signalfrom the intermediate frequency signal of the video intermediatefrequency band amplified by the intermediate frequency amplifier. Whenreceiving the FM radio broadcast, the first switch is switched towards aself-running oscillation signal, and the second switch is switchedtowards and connected to a second automatic gain controller. The tunerconverts the FM radio broadcast signal into an intermediate frequencythat is the same as the sound intermediate frequency subcarrier signalwhen receiving the television broadcast signal and outputs it whenreceiving the FM radio broadcast signal. The band limit filter passesthis intermediate frequency, and the intermediate frequency is amplifiedby the intermediate frequency amplifier. On this occasion, theintermediate frequency amplifier is gain controlled so that theamplitude of the sound subcarrier signal that the sound band limitfilter outputs is made constant by the second automatic gain controller.After this, the video detector detects and outputs the sound subcarriersignal from the intermediate frequency signal of the video intermediatefrequency band amplified by the intermediate frequency amplifier. Onthis occasion, the video detector detects and outputs the soundsubcarrier signal based on the self-running oscillation signal that asecond phase synchronizer outputs which is provided independently of afirst phase synchronizer employed when receiving the televisionbroadcast signal. With this, the band limit filter of the exclusive useof sound, the intermediate frequency amplification circuit of theexclusive use of sound, and the intermediate frequency detection circuitof the exclusive use of sound become unnecessary. Further, detecting andoutputting a frequency is performed by the first phase synchronizer andthe second phase synchronizer each provided independently so thatquality deterioration of the sound signal due to unevenness in phasesynchronization when receiving the FM radio broadcast signal can berestrained.

[0012] Other objects and features of this invention will become apparentfrom the following description with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a block diagram which shows the structure of a receiverof a first embodiment of the present invention.

[0014]FIG. 2 is a block diagram which shows the structure of a receiverof a second embodiment of the present invention.

[0015]FIG. 3 is a block diagram which shows the structure of theoscillator of a receiver of a third embodiment of the present invention.

[0016]FIG. 4 is a block diagram which shows the structure of theoscillator of a receiver of a fourth embodiment of the presentinvention.

[0017]FIG. 5 is a block diagram which shows the structure of a receiverof a fifth embodiment of the present invention.

[0018]FIG. 6 is a block diagram which shows the structure of aconventional receiver.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Five preferred embodiments of a receiver according to the presentinvention will be explained here in detail referring to the attacheddrawings.

[0020]FIG. 1 is a block diagram which shows the structure of a receiverof a first embodiment of the present invention. An antenna 11 receives atelevision broadcast signal and an FM radio broadcast signal. A tuner 12tunes the signal received by the antenna 11. When receiving thetelevision broadcast signal, the tuner 12 converts the signal into anintermediate frequency signal including the modulation component of animage and the modulation component of sound and outputs it to a surfaceacoustic waves (SAW) filter 13. On the other hand, when receiving the FMradio broadcast signal, the tuner 12 converts the signal into anintermediate frequency signal with the same frequency as a soundintermediate frequency component when receiving the television broadcastsignal and outputs it to the SAW filter 13. The SAW filter 13 performs aband limit so as to pass a video intermediate frequency band and passesthe intermediate frequency signal.

[0021] Operations when receiving the television broadcast signal will beexplained. The intermediate frequency signal passing through the SAWfilter 13 is amplified to a constant level by a VIF amplifier 14 and isoutputted to a video detector 16. The video detector 16 synchronouslydetects the intermediate frequency signal inputted from the VIFamplifier 14 by the signal of a video intermediate frequency carrierfrequency of outputted from a voltage control oscillator (VCO) 17 andoutputs a video signal as a detection output to a terminal 19 as well asa band pass filter 31.

[0022] When receiving the television broadcast signal, a switch 20 isconnected to a terminal that receives the output from the VIF amplifier14. Thus, the intermediate frequency signal of the VIF amplifier 14 isinputted into an automatic phase detector (APC) 18. The APC 18 comparesthe phase of the output signal of the voltage control oscillator (VCO)17 with the phase of the intermediate frequency signal inputted from theVIF amplifier 14 and outputs this phase difference to the VCO 17. TheVCO 17 outputs a signal corresponding to the video intermediatefrequency carrier frequency of to the video detector 16 based on thephase difference. That is, a phase synchronization loop is formed by theVCO 17 and the APC 18.

[0023] When receiving the television broadcast signal, a switch 42 isconnected to a terminal that receives the output of a VIF automatic gaincontrol (AGC) circuit 15. The VIFAGC circuit 15 controls the gain of theVIF amplifier 14 so that the video signal outputted from the videodetector 16 has a constant amplitude.

[0024] Here, suppose that the video intermediate frequency carrierfrequency is “fo” and the sound subcarrier frequency is “fs,” then thesound intermediate frequency subcarrier frequency is “of-fs.” Since theoscillation frequency from the VCO 17 is the video intermediatefrequency carrier frequency of, the sound subcarrier frequency fs isincluded in the video signal outputted from the video detector 16.

[0025] The band pass filter 31 extracts the signal of the soundsubcarrier frequency fs and outputs it to an SIF amplifier 32. The SIFamplifier 32 amplifies the sound subcarrier frequency fs and outputs itto an FM detector 33. The FM detector 33 FM detects the signal of thesound subcarrier frequency fs and converts it to a sound signal tooutput it to a terminal 34 as a sound output.

[0026] Next, operations when receiving the FM radio broadcast signalwill be explained. The intermediate frequency signal passing through theSAW filter 13 is amplified to a constant level by the VIF amplifier 14and is outputted to the video detector 16. The video detector 16synchronously detects the intermediate frequency signal inputted fromthe VIF amplifier 14 by the signal of the oscillation frequency ofcorresponding to the video intermediate frequency carrier frequency ofoutputted from the VCO 17 and outputs an FM intermediate frequency fscorresponding to the sound subcarrier frequency fs when receiving thetelevision broadcast signal to the band pass filter 31.

[0027] Since the video intermediate frequency carrier frequency of isnot included in the intermediate frequency outputted from the VIFamplifier 14, the FM intermediate frequency fs cannot be stabilized.Therefore, by switching the switch 20 to a terminal that receives theoutput of an oscillator 40, the self-running oscillation frequency ofcorresponding to the video intermediate frequency carrier frequency ofthat the oscillator 40 outputs is inputted into the APC 18 so that theAPC 18 and the VCO 17 form a phase synchronization loop to output theoscillation frequency of that is phase locked to the video detector 16.The video detector 16, employing this oscillation frequency of,generates the FM intermediate frequency fs and outputs it to the bandpass filter 31.

[0028] The band pass filter 31 extracts the signal of the FMintermediate frequency fs similarly to when receiving the televisionbroadcast signal and outputs it to the SIF amplifier 32. The SIFamplifier 32 amplifies the inputted FM sound intermediate frequency fsand outputs it to the FM detector 33. The FM detector 33 FM detects thesignal of the inputted FM sound intermediate frequency fs and convertsit into a sound signal to output it as a sound output to the terminal34.

[0029] When receiving the FM radio broadcast signal, the switch 42 isconnected to an AGC circuit 41 side. The AGC circuit 41 controls thegain of the VIF amplifier 14 so that the FM sound intermediate frequencyfs outputted from the band pass filter 31 has a constant amplitude.

[0030] Thus, when receiving the FM radio broadcast signal, the tuner 12outputs the intermediate frequency that is the same as the intermediatefrequency when receiving the television broadcast signal. The videosignal and the sound signal of the television broadcast signal and thesound signal of the FM radio broadcast signal are demodulated using asingle SAW filter 13. Therefore, there is no need to provide the SAWfilter 121 of the exclusive use of sound, the intermediate frequencyamplifier circuit 122 of the exclusive use of sound, the intermediatefrequency detection circuit 124 of the exclusive use of sound, and theintermediate frequency AGC circuit 123 of the exclusive use of sound,which are provided in a conventional receiver. Thus, a receiver can berealized through a simple structure, and a lightweight miniaturizationcan be facilitated.

[0031] Further, since gain control is performed for the intermediatefrequencies respectively corresponding to that when receiving thetelevision broadcast signal and when receiving the FM radio broadcastsignal, stable demodulation processing can be performed.

[0032] Next, a second embodiment of the present invention will beexplained. In the first embodiment described above, the video detector16 detects and outputs the FM sound intermediate frequency fs, employingthe self-running oscillation frequency of corresponding to the videointermediate frequency carrier frequency of which is phase locked by theoscillator 40, the APC 18, and the VCO 17 when receiving the FM radiobroadcast signal. However, in this second embodiment, a tuner 12 agenerates an intermediate frequency having a high passing gain for theSAW filter 13 when receiving the FM radio broadcast signal, and anoscillator 40 a outputs an oscillation frequency foB by which the FMsound intermediate frequency fs can be detected and outputted withrespect to this intermediate frequency to the video detector 16.

[0033]FIG. 2 is a block diagram which shows the structure of a receiverof the second embodiment of the present invention. The receiver isprovided with a tuner 12 a instead of the tuner 12 shown in the firstembodiment. Further, an oscillator 40 a is provided instead of theoscillator 40. Other components are the same as those explained inconnection with the first embodiment, they have be provided with thesame legends.

[0034] Generally, the SAW filter 13 for a band limit used in anintermediate frequency processing circuit employed in a receiverreceives the signal which is remaining side band modulated. Thus, gainincrement of the remaining part exists, and the gain of the gainincrement part is regulated. Therefore, there is attenuation of −6 dB atthe video carrier intermediate frequency of, and there is attenuation ofapproximately −6 to −10 dB at the sound subcarrier frequency (of-fs).When the intermediate frequency of the FM radio broadcast signal isreceived employing the SAW filter 13 having that type of attenuationcharacteristics, sensitivity loss of approximately −6 to −10 dB isgenerated compared with the central part of the passing band of the SAWfilter 13.

[0035] Accordingly, in this second embodiment, when the FM radiobroadcast signal is received, the tuner 12 a outputs an intermediatefrequency fsx passing through the central part of the passing band ofthe SAW filter 13. In order to detect the FM sound intermediatefrequency fs relative to this intermediate frequency fsx, the oscillator40 a oscillates the oscillation frequency foB and outputs theoscillation frequency foB outputted by the phase synchronization loopcircuit formed by the APC 18 and the VCO 17 to the video detector 16.

[0036] This oscillation frequency foB satisfies one of the followingequations (1) or (2).

foB=fsx+fs   (1)

foB=fsx−fs   (2)

[0037] The switch 20 is connected to the terminal that receives theoutput of the VIF amplifier 14 when receiving the television broadcastsignal. Therefore, the video intermediate carrier frequency of in whichthe VCO 17 is phase locked is input into the video detector 16. Thevideo detector 16 detects and outputs the video signal and the soundsubcarrier frequency fs. The switch 20 is connected to the terminal thatreceives the output of the oscillator 40 a when receiving the FM radiobroadcast signal. Therefore, the oscillation frequency foB in which theVCO 17 is phase locked is input into the video detector 16. The videodetector 16 detects and outputs the FM sound intermediate frequency fs.In this case, by setting the intermediate frequency fsx inputted to thevideo detector 16 at a frequency of the central part of the passing bandof the SAW filter 13, there is no attenuation in gain, and the frequencyfsx is inputted to the video detector 16 so as to detect and output theFM sound intermediate frequency with a low sensitivity loss. Theintermediate frequency fsx may be set to a part in which the gainattenuation of the passing band of the SAW filter 13 is small, and asfar as this condition is satisfied, the frequency fsx can be set as anarbitrary intermediate frequency fsx.

[0038] Thus, when receiving the FM radio broadcast signal, the tuner 12a generates the intermediate frequency fsx in which there is no gainattenuation for the passing band of the SAW filter 13, and theoscillator 40 a outputs an arbitrary oscillation frequency foB by whichthe FM sound intermediate frequency fs can be detected and outputtedrelative to that intermediate frequency fsx to the video detector 16side. Therefore, the FM sound intermediate frequency fs with a lowsensitivity loss can be detected and outputted.

[0039] A third embodiment of the present invention will now beexplained. In this third embodiment, the oscillator 40 a shown in thesecond embodiment described above is efficiently formed.

[0040]FIG. 3 is a block diagram which shows the structure of theoscillator 40 a applied to a receiver of the third embodiment of thepresent invention. This oscillator 40 a can be used as the oscillator 40a in the second embodiment. This oscillator 40 a is a phasesynchronization loop circuit composed of a VCO 51, an APC 52, and afrequency divider 53. This oscillator 40 a generates and outputs theoscillation frequency foB of 39.38 MHz based on a color signalsubcarrier frequency fsc of 3.58 MHz employed in color signaldemodulation incorporated in a receiver of an NTSC system.

[0041] In case of NTSC system, the color signal subcarrier frequency fscof 3.58 MHz is stably generated inside the receiver. This color signalsubcarrier frequency fsc is inputted into the APC 52. The APC 52 detectsthe phase difference between the frequency obtained by dividing theoscillation frequency foB outputted from the VCO 51 into 11 by means ofthe frequency divider 53 and the color signal subcarrier frequency fscand outputs it to the VCO 51. The VCO 51 performs phase control for theoscillation frequency foB based on that phase difference, and outputs itto the APC 18.

[0042] When the oscillation frequency foB of 39.38 MHz is employed, theintermediate frequency fsx when receiving the FM radio broadcast signalbecomes as follows according to the equation (1). $\begin{matrix}{{fsx} = \quad {{foB} + {fs}}} \\{= \quad {{39.38\quad {MHz}} + {4.5\quad {MHz}}}} \\{= \quad {43.88\quad {MHz}}}\end{matrix}$

[0043] Here, when the SAW filter 13 has a characteristic that the videointermediate frequency band having a video intermediate carrierfrequency of of 45.75 MHz employed in North American area is passed,this intermediate frequency fsx is located in approximately the centerof the passing band of the SAW filter 13. Since there is no gainattenuation, the FM sound intermediate frequency fs having a lowsensitivity loss can be produced and outputted.

[0044] Thus, since the oscillation frequency foB is generated utilizingthe color signal subcarrier frequency fsc of 3.58 MHz incorporated in areceiver, providing a special oscillation source is not necessary, andthe interactions and effects of the second embodiment described abovecan be obtained through a simple structure.

[0045] A fourth embodiment of the present invention will be explained.The third embodiment can be applied only to the case in which the SAWfilter 13 passing the video intermediate frequency band having the videointermediate carrier frequency of of 45.75 MHz employed in NorthAmerican area is employed. However, in this fourth embodiment, even whenthe SAW filter 13 passing the video intermediate frequency band having avideo intermediate carrier frequency of of 58.75 MHz mainly used inJapan is employed, the second embodiment can be realized through asimple structure.

[0046]FIG. 4 is a block diagram showing the structure of the oscillator40 a applied to a receiver of the fourth embodiment of the presentinvention. This oscillator 40 a may be used as the oscillator 40 a inthe second embodiment. This oscillator 40 a is provided with a frequencydivider 54 dividing the output of the VCO 51 into 44 as a substitute forthe frequency divider 53 shown in the third embodiment, and a frequencydivider 55 dividing the color signal subcarrier frequency fsc of 3.5 MHzinto 3 or 4 and outputting this divided output to the APC 52. Frequency⅓ or ¼ dividing by means of this frequency divider 55 is switchinglyset. Other components are the same as that of the second ad thirdembodiments.

[0047] First, a case will be explained wherein the SAW filter 13 passingthe video intermediate frequency band having the video intermediatecarrier frequency of of 45.75 MHz employed in North American area isemployed. In this case, the frequency divider 55 is switchingly set for¼ frequency dividing. The frequency divider 55 divides the inputtedcolor signal subcarrier frequency fsc of 3.58 MHz into 4(¼ timesfrequency) and outputs it to the APC 52. The APC 52 detects the phasedifference between the signal outputted from the frequency divider 55and the signal obtained by dividing the output of the VCO 51 into 44 bymeans of the frequency divider 54 and outputs it to the VCO 51. The VCO51 phase locks the oscillation frequency foB of 39.38 MHz that is 44/4times (11 times) the color signal subcarrier frequency fsc based on thatphase difference and outputs it to the APC 18.

[0048] In this case, similarly to the third embodiment, the intermediatefrequency fsx when receiving the FM radio broadcast signal becomes asfollows according to the equation (1). $\begin{matrix}{{fsx} = \quad {{foB} + {fs}}} \\{= \quad {{39.38\quad {MHz}} + {4.5\quad {MHz}}}} \\{= \quad {43.88\quad {MHz}}}\end{matrix}$

[0049] Since this intermediate frequency fsx is located in approximatelythe center of the passing band of the SAW filter 13 employed in NorthAmerican area and there is no gain attenuation, the FM soundintermediate frequency fs having a low sensitivity loss can be generatedand outputted.

[0050] When the SAW filter 13 passing the video intermediate frequencyband having the video intermediate carrier frequency of of 58.75 MHzemployed mainly in Japan is used, the frequency divider 55 isswitchingly set for ⅓ frequency dividing. The frequency divider 55divides the inputted color signal subcarrier frequency fsc of 3.58 MHzinto 4 (¼ times frequency) and outputs it to the APC 52. The APC 52detects the phase difference between the signal outputted from thefrequency divider 55 and the signal obtained by dividing the output ofthe VCO 51 into 44 by means of the frequency divider 54 and outputs itto the VCO 51. The VCO 51 phase locks the oscillation frequency foB of52.5 MHz that is 44/3 times the color signal subcarrier frequency fscbased on that phase difference and outputs it to the APC 18.

[0051] In this case, the intermediate frequency fsx of the time ofreceiving the FM radio broadcast signal becomes as follows according tothe equation (1). $\begin{matrix}{{fsx} = \quad {{foB} + {fs}}} \\{= \quad {{52.5\quad {MHz}} + {4.5\quad {MHz}}}} \\{= \quad {57.0\quad {MHz}}}\end{matrix}$

[0052] Since this intermediate frequency fsx is located in approximatelythe center of the passing band of the SAW filter 13 employed mainly inJapan and there is no gain attenuation, the FM sound intermediatefrequency fs having a low sensitivity loss can be generated andoutputted.

[0053] Thus, the oscillation frequency foB can be produced utilizing thecolor signal subcarrier frequency fsc of 3.58 MHz incorporated in areceiver for either of receivers employed in North American area andJapan by switching setting of the frequency divider 55. Accordingly,there is no need to provide a special oscillation source, and theinteractions and effects of the second embodiment described above can beobtained through a simple structure.

[0054] A fifth embodiment of the present invention will now beexplained. FIG. 5 is a block diagram which shows the structure of areceiver of the fifth embodiment of the present invention. This receivercomprises a phase synchronization loop circuit which phase locks theoscillation frequency foB that the oscillator 40 a outputs in additionto a phase synchronization loop circuit which outputs the oscillationfrequency of obtained by phase locking the video intermediate carrierfrequency of that the VIF amplifier 14 outputs to the video detector 16.Further, a switch 20 a selectively switches the respective phasesynchronization loop circuit outputs and outputting it to the videodetector 16. This switch 20 a is provided in place of the switch 20.Other components are the same as those explained in connection to thesecond embodiment.

[0055] The switch 20 a is connected to a terminal that receives theoutput of the VCO 17 while receiving the television broadcast signal andis connected to a terminal that receives the output of a VCO 43 whenreceiving the FM radio broadcast signal. When receiving the televisionbroadcast signal, the APC 18 detects the phase difference between thevideo intermediate carrier frequency of that the VIF amplifier 14outputs and the output of the VCO 17 and outputs this phase differenceto the VCO 17. The VCO 17 outputs the intermediate carrier frequency ofphase locked by this phase lock loop to the video detector 16 via theswitch 20 a.

[0056] When receiving the FM radio broadcast signal, the APC 44 detectsthe phase difference between the oscillation frequency foB outputtedfrom the oscillator 40 a and the output of the VCO 43 and outputs thisphase difference to the VCO 43. The VCO 43 outputs the oscillationfrequency foB phase locked by this phase lock loop to the video detector16 via the switch 20 a.

[0057] The oscillator 40 a may be constructed so as to performoutputting by employing the color signal subcarrier frequency fsc asexplained in the third and fourth embodiments. Further, as a substitutefor the oscillator 40 a, the oscillator 40 outputting the oscillationfrequency of may be employed. In the case in which this oscillator 40 isemployed, similar interactions and effects to the first embodiment areproduced.

[0058] Thus, since the phase synchronization circuit of the exclusiveuse of the oscillation frequency foB is provided, frequency drift due tounevenness in the oscillation frequency of the VCO 17 can be surelyrestrained, and a sound signal having a high quality can be outputtedwhen receiving the FM radio broadcast signal.

[0059] As described above, according to the receiver of one aspect ofthe present invention, when receiving the television broadcast signal,the video intermediate carrier signal that the intermediate frequencyamplifier outputs is selected by the first switch, and the second switchis switched and connected to the first automatic gain controller. Thetuner converts the television broadcast signal into an intermediatefrequency, and the band limit filter passes this intermediate frequencyso that the intermediate frequency is amplified by the intermediatefrequency amplifier. On this occasion, the intermediate frequencyamplifier is gain controlled so that the amplitude of the video signalthat the video detector outputs is made constant by the first automaticgain controller. When receiving the FM radio broadcast, the self-runningoscillation signal is selected by the first switch, and the secondswitch is switched and connected to the second automatic gaincontroller. The tuner converts the FM radio broadcast signal into anintermediate frequency that is the same as the sound intermediatefrequency subcarrier signal when receiving the television broadcastsignal and outputs it when receiving the FM radio broadcast signal. Theband limit filter passes this intermediate frequency, and theintermediate frequency is amplified by the intermediate frequencyamplifier. On this occasion, the intermediate frequency amplifier isgain controlled so that the amplitude of the sound subcarrier signalthat the sound band limit filter outputs is made constant by the secondautomatic gain controller. With this, the band limit filter of theexclusive use of sound, the intermediate frequency amplification circuitof the exclusive use of sound, and the intermediate frequency detectioncircuit of the exclusive use of sound become unnecessary, and a soundsignal having a high quality can be demodulated and outputted even whenreceiving the FM radio broadcast signal. Thus, an effect is producedwherein the a lightweight miniaturization of a receiver can befacilitated.

[0060] According to the receiver of another aspect of the presentinvention, when receiving the television broadcast signal, the videointermediate carrier signal that the intermediate frequency amplifieroutputs is selected by the first switch, and the second switch isswitched and connected to the first automatic gain controller. The tunerconverts the television broadcast signal into an intermediate frequency,and the band limit filter passes this intermediate frequency so that theintermediate frequency is amplified by the intermediate frequencyamplifier. On this occasion, the intermediate frequency amplifier isgain controlled so that the amplitude of the video signal that the videodetector outputs is made constant by the first automatic gaincontroller. After that, the video detector outputs the video signalcontaining the sound subcarrier signal from the intermediate frequencysignal of the video intermediate frequency band amplified by theintermediate frequency amplifier. When receiving the FM radio broadcast,the self-running oscillation signal is selected by the first switch, andthe second switch is switched and connected to the second automatic gaincontroller. The tuner converts the FM radio broadcast signal into anintermediate frequency that is the same as the sound intermediatefrequency subcarrier signal when receiving the television broadcastsignal and outputs it when receiving the FM radio broadcast signal. Theband limit filter passes this intermediate frequency, and theintermediate frequency is amplified by the intermediate frequencyamplifier. On this occasion, the intermediate frequency amplifier isgain controlled so that the amplitude of the sound subcarrier signalthat the sound band limit filter outputs is made constant by the secondautomatic gain controller. After this, the video detector detects andoutputs the sound subcarrier signal from the intermediate frequencysignal of the video intermediate frequency band amplified by theintermediate frequency amplifier. On this occasion, the video detectordetects and outputs the sound subcarrier signal based on theself-running oscillation signal that the second phase synchronizeroutputs which is provided independently of the first phase synchronizeremployed when receiving the television broadcast signal. With this, theband limit filter of the exclusive use of sound, the intermediatefrequency amplification circuit of the exclusive use of sound, and theintermediate frequency detection circuit of the exclusive use of soundbecome unnecessary. Further, detecting and outputting a frequency isperformed by the first phase synchronizer and the second phasesynchronizer each provided independently so that quality deteriorationof the sound signal due to unevenness in phase synchronization whenreceiving the FM radio broadcast signal can be restrained. Thus, effectsare produced wherein the a lightweight and small size receiver can beobtained, and a sound signal having a high quality can be outputted.

[0061] Further, the tuner converts the FM radio broadcast signal into asound intermediate frequency carrier signal that is the passing band ofthe band limit filter and is an intermediate frequency signal havinghigh gain and outputting it when receiving the FM radio broadcastsignal, and the oscillator oscillates a self-running oscillation signalobtained by shifting the frequency of the sound intermediate frequencycarrier signal by the amount of the sound subcarrier frequency so thatthe intermediate frequency of the FM radio broadcast signal passesthrough the frequency band that is the passing band of the band limitfilter and in which the attenuation of the gain is small. Thus, aneffect is produced wherein a sound signal having a high sensitivity ofthe FM radio broadcast signal can be outputted.

[0062] Further, the producing unit produces a color signal subcarrierfrequency signal employed in the NTSC system, and the oscillator phaselocks and outputs an oscillation signal having a frequency of 11 timesthe color signal subcarrier frequency signal so that the color signalsubcarrier frequency signal that a receiver of an NTSC system typicallyincorporates is effectively utilized. Thus, an effect is producedwherein the a lightweight miniaturization of a receiver can be furtherfacilitated.

[0063] Further, the producing unit produces a color signal subcarrierfrequency signal employed in the NTSC system, and the oscillatorselectively switches and outputs the oscillation frequency of 44/3 timesthe color signal subcarrier frequency signal or the oscillationfrequency of 44/4 times the color signal subcarrier frequency signal sothat the color signal subcarrier frequency signal that a receiver of anNTSC system typically incorporates is effectively utilized. Thus,effects are produced wherein the a lightweight miniaturization of areceiver can be further facilitated, and receivers used in European andAmerican regions and mainly in Japan can be flexibly dealt with.

[0064] Although the invention has been described with respect to aspecific embodiment for a complete and clear disclosure, the appendedclaims are not to be thus limited but are to be construed as embodyingall modifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

What is claimed is:
 1. A receiver by which a television broadcast signaland an FM radio broadcast signal can be selectively received,demodulated, and outputted, said receiver comprising: a tuner whichconverts the FM radio broadcast signal into an intermediate frequencysignal that is the same as a sound intermediate frequency subcarriersignal when receiving the television broadcast signal and outputs theintermediate frequency signal when receiving the FM radio broadcastsignal; a band limit filter which passes only an intermediate frequencysignal of a video intermediate frequency band of the televisionbroadcast signal among intermediate frequency signals output by saidtuner; an intermediate frequency amplifier which amplifies theintermediate frequency signal of the video intermediate frequency bandoutput by said band limit filter; an oscillator which oscillates andoutputs a self-running oscillation signal having the same frequency as avideo intermediate carrier signal of the video intermediate frequencyband; a first switch selects the video intermediate carrier signaloutput by said intermediate frequency amplifier when receiving thetelevision broadcast signal and selects the self-running oscillationsignal when receiving the FM radio broadcast signal; a phasesynchronizer which generates a signal that has a phase locked to thephase of the video intermediate carrier signal or the self-runningoscillation signal selected by said first switch; a video detector whichoutputs a video signal containing a sound subcarrier signal or a soundsubcarrier signal from the intermediate frequency signal of the videointermediate frequency band amplified by said intermediate frequencyamplifier based on the signal output by said phase synchronizer; a soundband limit filter which passes the sound subcarrier signal output bysaid video detector outputs; a sound detector which detects and outputsa sound signal of the television broadcast signal or a sound signal ofthe FM radio broadcast signal based on the sound subcarrier signaloutput by said sound band limit filter; a first automatic gaincontroller which changes the amplification factor of the intermediatefrequency amplifier when receiving the television broadcast and controlsthe amplitude of the video signal output by said video detector outputsto a constant value; a second automatic gain controller which changesthe amplification factor of the intermediate frequency amplifier whenreceiving the FM radio signal and controls the amplitude of the soundsubcarrier signal output by said sound band limit filter to a constantvalue; and a second switch which switches between the control by thefirst automatic gain controller and the control by the second automaticgain controller and outputs either control.
 2. The receiver according toclaim 1, wherein said tuner converts the FM radio broadcast signal intoa sound intermediate frequency carrier signal that is the passing bandof said band limit filter and is an intermediate frequency signal havinghigh gain and outputting it when receiving the FM radio broadcastsignal, and said oscillator oscillates a self-running oscillation signalobtained by shifting the frequency of the sound intermediate frequencycarrier signal by the amount of the sound subcarrier frequency.
 3. Thereceiver according to claim 1 further having a producing unit whichproduces a color signal subcarrier frequency signal employed in the NTSCsystem, wherein said oscillator is a phase synchronization loop circuitthat phase locks and outputs an oscillation signal having a frequencywhich is 11 times of the color signal subcarrier frequency signal. 4.The receiver according to claim 1 further having a producing unit whichproduces a color signal subcarrier frequency signal employed in the NTSCsystem, and said oscillator having a first frequency dividing unit whichdivides the color signal subcarrier frequency signal into 3; a secondfrequency dividing unit which divides the color signal subcarrierfrequency signal into 4; a selection switch which selectively switchesthe output of said first frequency dividing unit or the output of saidsecond frequency dividing unit; and a phase synchronization loop circuitwhich phase locks and outputs the oscillation signal having a frequencywhich is 44 times of the output signal selectively switched by theselection switch.
 5. A receiver by which a television broadcast signaland an FM radio broadcast signal can be selectively received,demodulated, and outputted, said receiver comprising: a tuner whichconverts the FM radio broadcast signal into an intermediate frequencysignal that is the same as a sound intermediate frequency subcarriersignal when receiving the television broadcast signal and outputs theintermediate frequency signal when receiving the FM radio broadcastsignal; a band limit filter which passes only an intermediate frequencysignal of a video intermediate frequency band of the televisionbroadcast signal among intermediate frequency signals output by saidtuner; an intermediate frequency amplifier which amplifies theintermediate frequency signal of the video intermediate frequency bandoutput by said band limit filter; an oscillator which oscillates andoutputs a self-running oscillation signal having the same frequency as avideo intermediate carrier signal of the video intermediate frequencyband; a first phase synchronizer which phase locks to the videointermediate carrier signal; a second phase synchronizer which phaselocks to the self-running oscillation signal; a first switch whichselects the output of said first phase synchronizer when receiving thetelevision broadcast signal and selects the self-running oscillationsignal when receiving the FM radio broadcast signal; a video detectorwhich outputs a video signal containing a sound subcarrier signal or asound subcarrier signal from the intermediate frequency signal of thevideo intermediate frequency band amplified by said intermediatefrequency amplifier, employing the output of said first switch; a soundband limit filter passing the sound subcarrier signal output by saidvideo detector; a sound detector which detects and outputs a soundsignal of the television broadcast signal or a sound signal of the FMradio broadcast signal based on the sound subcarrier signal output bysaid sound band limit filter; a first automatic gain controller whichchanges the amplification factor of said intermediate frequencyamplifier when receiving the television broadcast and controls theamplitude of the video signal output by said video detector to aconstant value; a second automatic gain controller which changes theamplification factor of the intermediate frequency amplifier whenreceiving the FM radio signal and controls the amplitude of the soundsubcarrier signal output by said sound band limit filter to a constantvalue; and a second switch which switches between the control by saidfirst automatic gain controller and the control by the second automaticgain controller and outputting either control.
 6. The receiver accordingto claim 5, wherein said tuner converts the FM radio broadcast signalinto a sound intermediate frequency carrier signal that is the passingband of said band limit filter and is an intermediate frequency signalhaving high gain and outputting it when receiving the FM radio broadcastsignal, and said oscillator oscillates a self-running oscillation signalobtained by shifting the frequency of the sound intermediate frequencycarrier signal by the amount of the sound subcarrier frequency.
 7. Thereceiver according to claim 5 further having a producing unit whichproduces a color signal subcarrier frequency signal employed in the NTSCsystem, wherein said oscillator is a phase synchronization loop circuitthat phase locks and outputs an oscillation signal having a frequencywhich is 11 times of the color signal subcarrier frequency signal. 8.The receiver according to claim 5 further having a producing unit whichproduces a color signal subcarrier frequency signal employed in the NTSCsystem, and said oscillator having a first frequency dividing unit whichdivides the color signal subcarrier frequency signal into 3; a secondfrequency dividing unit which divides the color signal subcarrierfrequency signal into 4; a selection switch which selectively switchesthe output of said first frequency dividing unit or the output of saidsecond frequency dividing unit; and a phase synchronization loop circuitwhich phase locks and outputs the oscillation signal having a frequencywhich is 44 times of the output signal selectively switched by theselection switch.